Methods for manufacturing organic light-emitting diodes (LEDs) are broadly divided into vacuum deposition methods and coating methods. Among them, coating methods have advantages such as easiness of large-area film formation and high material-use efficiency. When a coating method is to be used to form an organic LED, it is required that the number of layers in the organic LED is smaller, and its light-emitting layer is a single-layer structure.
PTL 1 has reported, as an organic, white light-emitting device, a single layer-type white light-emitting organic EL device including electrodes and a light-emitting layer with a single-layer structure disposed between the electrodes. In this light-emitting device, the light-emitting layer includes a composition including at least (a) a polymer and (b) emission center-forming compounds. This composition contains an electron-transporting material and a hole-transporting material in a good balance. The polymer emits blue light or light with a wavelength shorter than blue. Molecules of two or more of the emission center-forming compounds are dispersed in the polymer. Each emission center-forming compound emits light by itself. The two or more emission center-forming compounds are used in combination so that light beams emitted from the whole of the organic EL device appear white. Besides PTL 1, related published literatures include PTL 2 and PTL 3.